This invention relates to multiple imaging, and, more particular to imaging which produces different images from different viewing angles.
The production of images which change with a change in viewing angle has been known for many years. It is described, for example, by V. G. Anderson in U.S. Pat. No. 2,815,310. The images are produced on opaque or transparent sheets of material such as paper, paper board or plastic. The resulting imprint, in black and white or color, is laminated to a transparent lenticular lens. Alternatively, a transparent plastic carrier may be printed on its reverse side and viewed through a lenticular lens face of the carrier.
A lenticular screen, as is well known, has a number of lenses arranged in side-by-side relationship. Each lens, commonly termed a lenticle, may be formed by an elongated or circular convex frontal surface, and a flat rear surface
The printed image is formed by two interleaved pictures producing a grid of parallel lines with alternating striations. The pitch, or number of picture-element pairs per unit distance, must be the same as the lens pitch of the lenticular array. In addition, the focal length of each lenticles should be equal to the thickness of the lenticular sheet Under these conditions, at one viewing angle an observer will see only one picture, while at a different angle the same observer will see the other picture.
The requirement that the picture elements be in registration with the lenticular array complicates the printing and lens forming steps. In practice, the pitch of the lenticular assembly is limited to a spacing that is equivalent to 100 lenticles per inch, or less. Even with 50-100 lenticles per inch, it is difficult to hold the registration over widths of more than a few inches. This limitation restricts the quality of pictorial resolution, as well as size.
Because of the required image registration, the cost of producing articles is substantial. In addition, the focal length of the lenticles must equal the thickness of the lenticular sheet. At a pitch of 100 lenticles per inch, assuming a half cylinder lenticular surface, the focal length for a conventional plastic sheet, having refractive index of 1.5 to 1.6 is 0.016 to 0.019 inches. The result is a relatively thick sheet that not only can have objectionable bulk but also increases the final cost of the article.
Accordingly, it is an object of the invention to facilitate multiple imaging using a lenticular sheet. A related object is to facilitate lenticular imaging at different viewing angles.
Another object of the invention is to overcome difficulties associated with the registration of picture elements in a lenticular array. A related object is to simplify printing of lenticular sheets. Another related object is to facilitate interaction between picture elements and a lenticular array.
Still another object of the invention is to improve the pictorial resolution of images associated with lenticular arrays. A related object is to achieve improved quality at a substantial reduction in cost.
A further object of the invention is to reduce the thickness of lenticular sheets associated with multiple imaging. A correlated object is to eliminate the need for thick lenticular sheets in multiple imaging.